The Boss RT-20 Rotary Sound Processor is a pedal that uses BOSS’s COSM modelling to emulate the behaviour of a rotary speaker system, complete with adjustable horn and bass rotor speeds. It offers four modes of rotary effect (including standard rotary, rock-orientated tones, and UNI-V style modulation) and includes a Drive Type switch so it can be optimised for guitar or keyboard input. The pedal also features various knobs: MODE, RISE TIME (how fast the rotors switch speeds), FAST SPEED, SLOW SPEED, OVERDRIVE, BALANCE (between treble horn and bass rotor), DIRECT LEVEL, and EFFECT LEVEL. It provides multiple connectors: two mono inputs (INPUT A/B), stereo outputs (OUTPUT A/B), a PHONES jack, a SPEED jack for an expression pedal to control rotor speed in real time, and a DC 9V power input (or it runs on six AA batteries). The input impedance is 1 MΩ, the output impedance 1 kΩ, and it draws about 85 mA when powered at 9V. Recommended load impedance is 10 kΩ or greater. It has a “Virtual Rotor” display that visually represents the horn rotor (centre) and bass rotor (outer ring) in real time. Its controls include an on/off footswitch, a slow/fast footswitch (to swap rotor speeds), several knobs for shaping the effect, and indicators for power, effect status, and slow/fast state. The pedal measures 173 x 158 x 57 mm and weighs about 1.1 kg.
